1. Field of the Invention
This invention relates to a gear noise evaluation system, and in particular to a system for absolutely evaluating gear noises generated from a transmission in a car.
2. The Prior Art
Gear noises of a transmission have been so far evaluated sensually by those who have undergone an advanced training. One example of such a sensual or sensory evaluation is indicated in the following Table 1.
TABLE 1 __________________________________________________________________________ EXAMPLE OF SENSUAL GEAR NOISE EVALUATION POINT CONTENTS __________________________________________________________________________ 10 EXCELLENT NOT NOTICEABLE EVEN BY TRAINED EVALUATORS 9 VERY GOOD NOTICABLE ONLY BY TRAINED EVALUATORS 8 GOOD NOTICABLE ONLY BY CRITICAL CUSTOMERS 7 SATISFACTORY NOTICABLE BY ALL CUSTOMERS 6 AGREEABLE RATED DUSTURBING BY SOME CUSTOMERS 5 MEDIOCRE RATED DISTURBING BY ALL CUSTOMERS .uparw. IN ABOVE, SHIPMENT IS ALLOWABLE. 4 POOR RATED AS FAILURE BY ALL CUSTOMERS 3 VERY POOR COMPLAINED AS BAD FAILURE BY ALL CUSTOMERS 2 BAD LIMITED OPERATION 1 VERY BAD NON OPERATION __________________________________________________________________________
Taking examples in Table 1, such gear noises as even a highly trained inspector can not hear are evaluated as Point 10, and such gear noises as all customers recognize as noises or disturbing sounds are evaluated as Point 5. For a transmission generating the gear noises evaluated as Point 5 or above, for example, the shipment thereof is allowable.
It is to be noted that such a sensual evaluation by a highly trained inspector can be realized for each gear position (stage).
On the other hand, such gear noises as all customers feel noisy are evaluated as Point 4, and such gear noises as generated when the gear fails to operate at all are evaluated as Point 1.
Different from a humanly sensual evaluation as indicated above, there has been also adopted a relative evaluation system using an instrument such as an FFT (Fast Fourier Transform) analyzer i.e. Frequency Analyzer.
FIG. 7 shows a prior art gear noise evaluation system using such an instrument. A transmission 1 is connected to an input shaft 2 and an output shaft 3. The input shaft 2 is connected to an engine (not shown) and the output shaft 3 is connected to wheels (not shown) of a car.
A rotative speed sensor, rotational frequency sensor, or tachometer (hereinafter referred to as tachometer) 4 is provided so as to detect the rotative speed (rpm) of the output shaft 3 or the input shaft 2, and a microphone 5 is provided so as to detect the gear noise of the transmission 1.
The output signals of the tachometer 4 and the microphone 5 are received by the FFT analyzer 6 having a display screen displaying sound pressures of a gear noise at each gear position and of an overall noise with respect to rotative speeds, as shown in FIG. 8. It is to be noted that this display screen shows a characteristic of sound pressures with respect to rotative speeds at the primary engagement frequency.
The output signal of the tachometer 4 is also supplied to a control bench 7 so that an operator 8 sitting in front of the control bench 7 may monitor the rotative speed of the output shaft 3.
Namely, it is not neccesary that the operator 8 is the sensual evaluator who performs such an evaluation as indicated in Table 1. While watching the rotative speed of the output shaft 3 indicated by the output signal of the tachometer 4 through a correspoding instrument equipped in the control bench 7, the operator 8 goes on increasing the rotative speed by e.g. 100 rpm, as shown in FIG. 8. Every time the rotative speed is manually increased, the rotative speed detected by the tachometer 4 and the gear noise taken from the microphone 5 are received as an input by the FFT analyzer 6.
From these input signals, the FFT analyzer 6 displays a frequency analysis of a gear noise (sound pressure) every engagement order as the rotative speed increases, as shown in FIG. 8.
Then, the operator 8 judges from the frequency analysis that the gear noise is large when the difference in sound pressure between the overall noise and the other gear noises is small or what the present gear noise is like depending on the waveform pattern.
It is therefore disadvantageous that the above sensual evaluation by an evaluator provides individually different results and the instrumental evaluation shown in FIG. 7 can not provide a quantatively accurate judgement.
Also, no correlation can be substantiated between such an evaluation in a laboratory as shown in FIG. 7 and corresponding noise measurements actually done in a car. Namely, the latter case has many kinds of noise mingled into a microphone and largely damages the correlation with the former case because it is quite different in conditions and environments, resulting in being impractical.